Various systems that provide warnings or advisory indications of the presence of terrain or obstacles are known. Among those systems include systems generally known as ground proximity warning systems for aircraft. Such systems mohitor the flight conditions of an aircraft and provide a warning if the flight conditions are such that an inadvertent contact with the ground is imminent. Among the flight conditions monitored by such systems are radio altitude and rate, barometric altitude and rate, airspeed, and flap and gear positions. The aforementioned parameters are monitored, and an advisory indication or a warning is generated when the relationship between the aforesaid conditions or parameters is such that ground impact is likely to occur. Typical examples of such systems are disclosed in U.S. Pat. Nos. 3,715,718, 3,925,751, 3,934,221, 3,934,222, 3,936,796, 3,944,968, 3,947,808, 3,947,810, 3,958,218, 3,958,219, 4,016,565, 4,030,065, 4,058,710, 4,060,793, 4,067,520, 4,071,894, 4,093,938, 4,107,681, 4,112,413, 4,121,287, 4,122,529, 4,135,143, 4,189,777, 4,215,334, 4,293,840, 4,319,218, 4,336,976 and 4,369,425, and Canadian Pat. No. 1,033,828.
While the above-described systems provide advisory and warning signals in the event of proximity to terrain, such systems generate warnings based solely on the flight conditions of the aircraft, and do not utilize navigation information. Consequently, the sensitivity of such systems must be adjusted to provide adequate warnings when a hazardous flight condition exists without generating false or nuisance warnings when there is no danger. Such an adjustment results in a compromise that may still cause nuisance warnings when flying over terrain unique to particular geographic areas and reduced warning times in other areas. One approach to improve the performance of such systems has been to modify the warning envelopes of the ground proximity warning system in accordance with the geographic location of the aircraft in order to optimize the warning criteria for the particular geographic area over which the aircraft is flying. An example of such a system is described in U.S. patent application Ser. No. 448,862, filed Dec. 10, 1982 by Bateman, et al. and assigned to the same assignee of the assignee of the present invention. In the system disclosed in the aforesaid application, the warning criteria are optimized to suit the terrain characteristics about various geographic areas, particularly the airports from which the aircraft is taking off or landing.
Another approach utilizing a geographical input is disclosed in U.S. Pat. No. 4,224,669. In the system disclosed in the aforesaid patent, a memory device is employed to store minimum safe altitudes by geographic coordinate areas. A navigational computer is used to determine the position of the aircraft, and a warning is given if the aircraft descends below the stored minimum safe altitude for the coordinate area in which the aircraft is flying. The system has a "worst case" and a "tactical" mode of operation. In the "worst case" mode, the minimum safe altitude is determined as a function of the highest terrain feature or obstacle within the geographic coordinate area of interest. In the "tactical" mode of operation, current flight conditions such as position, ground speed and ground track are used to define a minimum safe altitude based on the heights of terrain and obstacles immediately ahead of the projected flight path.
While these systems do provide warnings of the proximity of terrain or obstacles, none of the above-described systems provides information relating to the exact location or nature of the terrain or obstacle, nor of the type of action required to avoid the obstacle. Thus, when a warning representative of the proximity of terrain, or of a descent below a minimum safe altitude is provided by the above systems, the evasive action that is normally called for is for the pilot to pull up. While pulling up may be sufficient evasive action to avoid impact in many or most cases, there are cases where turning right or turning left in addition to or instead of pulling up would provide a greater margin of safety.